To the outside world, you’re a productive citizen. Some might even say you’re highly successful. But when the workday is done, your internal resources are spent. You beg off dinner with friends because the best you can do is plop onto the couch or dive into bed so you’ll be ready to take on tomorrow.

That’s what life is like when you have what’s sometimes called high-functioning depression. You make do, you get by, you appear to be handling things just fine–but you’re suffering inside.

High-functioning depression isn’t a true medical diagnosis; you won’t find it listed in the Diagnostic and Statistical Manual of Mental Disorders, the bible of the mental health profession. But it is popping up on treatment center websites and health blogs as a way to characterize people with low mood, low energy, and anxiety, experts say.

Most high-functioning types have dysthymia (also known as persistent depressive disorder), a low-grade depression marked by lagging energy or fatigue. These are people who are generally unhappy in life but don’t meet the definition of major depression, which is more severe. Dysthymia generally persists for two or more years. But if you have it, you probably slap on a brave face and go about your business.

Dysthymia can be difficult to diagnose because “it’s gradual and kind of sneaky,” Dr. Williamson says. He equates it to turning up the temperature in a room by one degree at a time. People often don’t recognize they have a problem until they’re sick of feeling blue all the time or until a stressful life event causes their emotions to boil over.

Even some people with major depression–the classic, episodic type that causes low mood or loss of interest or pleasure, among other symptoms­­–may be deemed high-functioning. They tend to be individuals with a lot of determination who are willing to endure significant symptoms without asking for help, Dr. Williamson explains.

Anthony Rothschild, MD, professor of psychiatry at the University of Massachusetts Medical School, believes people with major depression are “high-functioning” too. “They’re doctors and lawyers and judges ... and every walk of life, but they suffer,” he says. “They’re not reaching their potential.”

There’s no clinical test for high-functioning depression. But primary care doctors and mental health professionals do use various screening tools to assess patients’ depressive symptoms and functioning. For example, your doctor may ask questions like: Are you unhappy or blue? Do you cry a lot? Do you have low energy? Do you have sleep problems?

As part of a new patient evaluation, Dr. Rothschild often poses a simple question. “I’ll say, ‘What do you do for fun?’ And if they look at me, like, Where did you come from?, then I know they might very well be suffering from depression,” he says.

What qualifies as high-functioning depression is somewhat subjective. People often fill three or four main roles in their lives: vocation (meaning work or school); intimate partner or spouse; parent; and friend or community member, explains Michael Thase, MD, professor of psychiatry at the University of Pennsylvania Perelman School of Medicine and co-author of Beating the Blues: New Approaches to Overcoming Dysthymia and Chronic Mild Depression. Assessing how active you are in your roles can help a mental health professional gauge high-functioning depression, he says. “You may notice that there’s a hole in this person’s extracurricular life."

Steven Huprich, PhD, professor of psychology at University of Detroit Mercy, says there may be something in a person’s nature–“a particular type of negative self-image”–fueling his or her chronic unhappiness. “If somebody came to me and said, ‘I think I have high-functioning depression,’ chances are not only would I hear about mood symptoms, but I’d probably hear something about being kind of perfectionistic, feeling guilty a lot, feeling self-critical,” he says.

If you’re aware you’re not performing up to speed, you might also experience feelings of self-doubt, anxiety, and a loss of confidence, Dr. Williamson adds.

Unfortunately, it can be easy for people with high-functioning depression to fly under the radar because they hide their suffering well. Without support, there’s a lot of “loneliness and aloneness,” Dr. Williamson says.

But just because you’re getting by doesn’t mean you don’t need help. Since depression treatment is highly individualized, every person’s regimen will differ and may include lifestyle changes, talk therapy, and/or medication.

You might start by consulting your primary care doctor, contacting an employee assistance program, or calling a therapist. The important point, experts say, is to seek help, because depression is highly treatable.

“Where you start with treatment,” Dr. Williamson says, “is less important than the fact that you start.”